Generally, domestic sewage discharged from residential facilities and rainwater flowing via rainwater pipes pass through sewage pipes, are collected at a septic tank, and then transferred to a sewage treatment plant. However, in our country (in Korea), a combined sewage system is employed in which the domestic sewage and the rainwater are mixed and discharged together, which causes various problems.
In detail, in the case of the combined sewage system, since a flow velocity is slow due to a low incline needed for allowing sewage to flow, pollutants are easily deposited in such a way that residual pollutants are decomposed, thereby causing a bad odor.
However, since the rainwater pipe for allowing rainwater to flow is installed at the combined sewage system to have an open structure, as described above, the bad odor generated inside a sewage pipe may be dispersed toward residential areas or roads.
Accordingly, rainwater pipes near residential facilities, stores, and restaurants may be blocked using rubber plates to prevent the bad odor, effects of which fail to satisfy expectation. Particularly, when it rains, to prevent an overflow of sewage or rainwater, it is necessary to remove the rubber plates in such a way that the bad odor still remains.
Also, it may be considered to set a carrier adsorbing and removing bad-smelling materials afloat inside the sewage pipe. In this case, when amounts of sewage and rainwater increase, the carrier may be often swept away and it is hard to expect an effect of removing a bad odor.
On the other hand, recently, there is provided a method of installing fans with certain intervals to extract a bad odor in one direction. However, as described above, since a sewage pipe has an open structure connected to a rainwater pipe and a plurality of branch pipes and a length thereof is very great, it is very difficult to form negative pressure thereinside. Accordingly, in this condition, it is almost impossible to prevent dispersion of a bad odor by operating fans.
Also, a bad odor with high density, which is deposited for a long time and hardly ever floats, exists inside the sewage pipe. Since bad odor removal systems, which have been developed, are almost installed at upper parts of sewage pipes, certain limitations exist in removing the bad odor with high density.